In prior art joysticks for utility work vehicles it is known to detect the relative position of a movable part of the joystick, typically being provided with a handle, and a substantially stationary part of the joystick by means of a number of ordinary bar magnets arranged on the movable part and corresponding magnetic detectors, e.g. Hall effect sensors, arranged on the stationary part. Each of the magnetic detectors detects a magnetic flux generated by the corresponding bar magnet. Since the magnetic field generated by a bar magnet varies along the length of the magnet, the detected magnetic flux reflects the relative position between the movable part and the stationary part of the joystick. An output generated by the magnetic detectors is therefore indicative of the position of the joystick.
In a joystick the movable part normally performs angular movements relatively to the stationary part. Accordingly, the magnetic detectors follow curved paths relatively to the bar magnets. These curved paths cross the magnetic field lines in such a manner that the change in magnetic flux detected by a magnetic detector is markedly non-linear in response to the distance traveled by the magnetic detector. This is particularly a problem at positions at or near a neutral position of the joystick, where relatively large angular movements of the movable part results in relatively small variations in the detected magnetic flux, thereby leading to a relatively poor angular resolution. Previously, it has been attempted to solve the problems described above by means of software compensation. However, at positions at or near the neutral position considerable software compensation is necessary. This has the adverse effect that a small change in sensor output will be translated into a larger change in angle. Since there are several tolerances, e.g. air gap, which can vary during operation this means that the angular region defined as neutral can vary significantly. This may even compromise the safety of an application having the joystick mounted therein, e.g. a vehicle. Thus, even if a joystick is not operated, it may generate and send a signal indicating that it is, and the application may thereby start moving without an operator. This is very disadvantageous and possibly hazardous.
Furthermore, the non-linearity described above also has the consequence that a relatively large number of calibration points are necessary when calibrating the sensor, because a calibration curve is normally obtained by interpolating between measured calibration points, and when the calibration curve is markedly non-linear, a large number of calibration points are necessary in order to ensure that the interpolated parts of the calibration curve give a substantially correct image of the actual relationship between the detected magnetic flux and the relative position. This is a further disadvantage, since it adds to production costs.